Conventional communication networks often provide communication paths between source and destination network elements that include bi-directional line-switched rings. In these rings, traffic is provided in both directions to allow for protection of traffic in the event of a failure. These rings support working traffic and protection traffic.
Working traffic, which is provided through regular channels in one direction around the ring, has corresponding back-up channels for protection in the opposite direction such that the working traffic may be carried through a back-up channel in the event of a failure in the corresponding regular channel. Protection traffic is provided through the back-up channels such that, in the event of a failure for the working traffic, the protection traffic is pre-empted by the working traffic which has priority to use the back-up channels for protection.
Bi-directional line-switched rings may also support non-preemptible unprotected traffic (NUT). NUT is traffic that is provided either through a regular channel or through a back-up channel and that is neither protected nor pre-empted by a failure. Thus, using NUT, a failure in the channel carrying the traffic results in a loss of the transmission of the traffic through the ring. However, a failure in a corresponding channel does not pre-empt the NUT. With NUT on a regular channel, therefore, additional NUT may be provided through the corresponding protection channel, resulting in a doubling of available bandwidth for that traffic.
Because NUT provisioning is traditionally accomplished locally and independently at each node in the ring, reliable use of non-preemptible unprotected traffic through a bi-directional line-switched ring is limited by the NUT provisioning capabilities of every node that is a part of or is later added to the ring, as well as by the NUT provisioning performed independently at each of these nodes, which must be identical.
Thus, in order to carry non-preemptible unprotected traffic reliably through the ring, each node in the ring must be capable of provisioning the traffic channels as non-preemptible unprotected traffic. If even a single node in the ring is incapable of NUT provisioning, non-preemptible unprotected traffic may not be carried reliably by the ring due to the use of protection channels for that traffic which would be pre-empted during a failure. Similarly, each node in the ring must provide identical NUT provisioning of the channels. If even a single node in the ring provisions the channels differently, traffic misconnections may occur during protection switches.